Trailer hitch

ABSTRACT

A trailer hitch for heavy vehicles has a coupling housing arranged on the traction vehicle with a rear, vertical end piece from which extends an upper, forward protruding coupling yoke piece and a lower, forward protruding coupling yoke piece, between which a tow eye on a trailer and a tow ball arranged in the tow eye are intended to be secured by means of a coupling pin running through a hole in the tow ball. A principally vertical wedge ( 12 ) is arranged between both coupling yoke pieces ( 3, 4 ) in front of the rear end piece ( 2 ) and is so designed that the wedging action increases, i.e. the force of the wedge increases, as the wedge is pressed down. An intermediate piece ( 14 ), equipped partly with an upper, forward protruding part ( 15 ) and partly a lower, forward protruding part ( 17 ), is arranged between the wedge ( 12 ) and the tow ball ( 6 ), whereby the parts are intended to abut against an upper ( 16 ) and a lower ( 18 ) part of the tow ball. The wedge ( 12 ) exhibits a spring device ( 13 ) acting on its top and intending to press down the wedge.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention concerns a trailer hitch arrangement for heavyvehicles that comprises a tow ball, intended to be arranged between oneupper and one lower coupling yoke piece on the traction vehicle, and atow eye arranged on the outer end of a tow bar fitted to a trailervehicle, whereby the tow eye and the tow hook are intended to interactwhen the traction vehicle tows the trailer vehicle.

2. Description of the Background Art

Such trailer hitches are commonplace on the market today. One problemwith existing trailer hitches is that there is already inherent freeplay between the tow ball and tow eye. This fire play increases as thetrailer hitch is used, partly through normal wear and partly due tosand, earth and other dirt particles entering into the moving parts ofthe hitch.

The variation in load caused by the said free play between the tow balland the tow eye on the trailer vehicle is conveyed throughout thevehicle and is perceived as especially disturbing by the driver. Anotherconsiderable disadvantage with the said free play is that the entirepower train in the traction vehicle, i.e. propeller shaft, universaljoints, engine and gearbox will eventually be damaged by the variationin load.

SUMMARY OF THE INVENTION

The present invention intends to eliminate these problems and offer anew type of trailer hitch that provides a coupling between the tractionvehicle and the trailer vehicle without any free play. This is madepossible with a trailer hitch of the aforesaid type exhibiting thecharacteristics specified in the enclosed claims.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention will be described in more detailwith reference to the enclosed drawings, where FIG. 1 is a perspectiveview of the new trailer hitch and FIG. 2 is a vertical cross section ofthe hitch viewed from one side.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing, a new trailer hitch is illustrated thatexhibits a coupling housing 1, comprising a rear, vertical end piece 2,from which extends an upper, forward protruding coupling yoke piece 3and a lower, forward protruding coupling yoke piece 4. A tow eye 5 froma trailer and a tow ball 6 arranged inside the tow eye are intended tobe contained between these yoke pieces.

Underneath the upper coupling yoke piece 3 and on top of the lowercoupling yoke piece 4 are guides 7, 8, which are intended to steer thetow ball correctly to couple the trailer to the traction vehicle.Furthermore, the central part of the tow ball 6 has a vertical hole 9through it, into which a coupling pin 10 is inserted. This arrangementenables the tow ball 6 and the surrounding tow eye 5 to be securelyfastened to the traction vehicle.

The coupling pin 10 is intended to be inserted into the hole 9 of thetow ball 6 and extracted from the same via a suitably driven, e.g.pneumatic or hydraulic, lift cylinder 11 mounted on top of the uppercoupling yoke piece 3.

The rear parts of both coupling yoke pieces 3, 4 are joined to the endpiece 2. In front of this end piece is a vertical wedge 12 arrangedbetween both yoke pieces. The wedge is so designed that the wedgingaction increases, i.e. the wedge force in the direction of the tow ballincreases, as the wedge is pressed down. This downward pressure isachieved with a spring device 13, which acts on the top of the wedge 12.

The wedge 12 is intended to engage an intermediate piece 14, whichexhibits partly an upper, forward protruding part 15, which is intendedto abut against the top part 16 of the tow ball 6, and partly a lower,forward protruding part 17, which is intended to abut against the bottompart 18 of the tow ball 6. This means that the wedge 12 and theintermediate piece 14, which is steered with guides in the couplinghousing, will press the tow ball 6 against the coupling pin 10.

As the tow ball 6 and thereby the tow eye 5 are pressed against thecoupling pin 10 in this way, any free play found in the trailer hitchwill disappear. Should any wear arise, the wedge 12 will compensate forit automatically as the spring device 13 will press down the wedge.

The top of the wedge 12 is covered by a wedge cover 19 and its bottominteracts with a pneumatic cylinder 20, which is intended to press upthe wedge 12 against the action of the spring device 13 to facilitateuncoupling the traction vehicle. The wedge then abuts against a setscrew21 arranged in the wedge cover 19.

With the assistance of this setscrew 21, the wedge 12 and thereby alsothe intermediate piece 14 can thus be adjusted so that the tow ballacquires the correct position in relation to the coupling pin 10 so thatthe pin can move to a locked position.

Once the coupling pin 10 has locked, the pneumatic cylinder 20 willrelease, whereby the spring 13 will press down the wedge 12 so that theintermediate piece 14 presses against the tow ball 6.

In order to obtain good support of the tow eye 5 against the tow ball 6,the former is equipped with a bearing shell 22, which is thus appliedagainst the tow ball. To prevent sand and dirt entering the interactingparts of the tow ball and tow eye, they are completely enclosed by arubber gaiter 23.

The invention is, of course, not limited to the submitted andillustrated embodiment but can be modified within the framework of thefollowing claims.

What is claimed is:
 1. Trailer hitch for heavy vehicles comprising: (a)a coupling housing arranged on a traction vehicle comprising a rear,vertical end piece from which extends an upper, forward protrudingcoupling yoke piece and a lower, forward protruding coupling yoke piece,between which a tow eye on a trailer and a tow ball arranged in the toweye are intended to be secured with a coupling pin running through ahole in the tow ball; (b) a principally vertical wedge arranged betweenthe coupling yoke pieces in front of the rear end piece so that wedgingaction increases as the wedge is pressed down; (c) an intermediate pieceequipped partly with an upper, forward protruding part and partly with alower, forward protruding part, arranged between the wedge and the towball, whereby the parts are intended to abut against an upper and alower part of the tow ball; and (d) a spring device acting on the wedgeand intending to press down the wedge.
 2. Trailer hitch according toclaim 1, wherein the coupling pin runs through the tow ball and bothcoupling yoke pieces and is moved in and out of them by a liftingcylinder arranged on the upper coupling yoke piece.
 3. Trailer hitchaccording to claim 2, wherein the lifting cylinder is hydraulic. 4.Trailer hitch according to claim 2, wherein the lifting cylinder ispneumatic.
 5. Trailer hitch according to claim 2, further comprising apneumatic cylinder interacting with a bottom portion of the wedge topress the wedge against the force of the spring device to facilitateuncoupling the traction vehicle from the trailer.
 6. Trailer hitchaccording to claim 1, further comprising a pneumatic cylinderinteracting with a bottom portion of the wedge to press the wedgeagainst the force of the spring device to facilitate uncoupling thetraction vehicle from the trailer.